[c-nsp] BGP -- ADSL as failover link

[Steve Bertrand]

Hi all,

Out of curiosity...

I have a 100Mb fibre Ethernet connection, and an ADSL connection to a
single provider via one router at my end.

Currently, said provider maintains an EIGRP setup between our router and
their own, so when the LANx connection goes down, our /21 is transits
over the ADSL connection.

In the very near future, we need to make some significant hardware
changes, which will likely include eliminating EIGRP entirely.

So:
 		 -----------------------|
	 --------|ADSL			|
UPSTREAM<	 |			| <- our router
	 --------|LANx			|
		 -----------------------|

Given the following BGP example config, will it impact my upstream any
differently than a current EIGRP setup would?

My main question however, is, again, given the following config, would
having an ADSL connection as a redundant feed be a bad thing? If my
Fibre goes down, and given the BGP config that I have, the route won't
flap anywhere upstream from my upstream...right?

Perhaps I could have posted this to NANOG, however I thought this was
but just a humble 'small guy' question.

PS: I am looking for help, therefore I will not try to be obscure in any
way. This is the config that I came up with, and it works very well in
my lab. There are many people that deserve thanks for aiding my
knowledge on BGP, so thank you. I have much to learn, so scrutiny is
MOST welcome.

TIA,

Steve


---------

! BEGIN CONFIG
!
! NOTE: $ppp_gw  = remote end of PPPoE multi-link
!
router bgp 14270
!
 no synchronization
 bgp log-neighbor-changes
!
 network 208.70.104.0 255.255.248.0
!
 neighbor 208.113.10.210 remote-as 21570
 neighbor 208.113.10.210 description LANx Upstream peer
 neighbor 208.113.10.210 route-map LANX-IN in
 neighbor 208.113.10.210 route-map LANX-OUT out
 neighbor 208.113.10.210 maximum-prefix 1
!
 neighbor $ppp_gw remote-as 21570
 neighbor $ppp_gw description Dialer upstream peer
 neighbor $ppp_gw route-map DIALER-IN in
 neighbor $ppp_gw route-map DIALER-OUT out
 neighbor $ppp_gw maximum-prefix 1
!
!
ip route 208.70.104.0 255.255.248.0 Null0
!
!
ip prefix-list DIALER-IN description Inbound via Dialer
ip prefix-list DIALER-IN seq 1 permit 0.0.0.0/0
ip prefix-list DIALER-IN seq 5 deny 0.0.0.0/0 le 32
!
ip prefix-list DIALER-OUT description Outbound via Dialer
ip prefix-list DIALER-OUT seq 5 permit 208.70.104.0/21
ip prefix-list DIALER-OUT seq 10 deny 0.0.0.0/0 le 32
!
ip prefix-list LANX-IN description Inbound via LANx
ip prefix-list LANX-IN seq 1 permit 0.0.0.0/0
ip prefix-list LANX-IN seq 5 deny 0.0.0.0/0 le 32
!
ip prefix-list LANX-OUT description Outbound via LANx
ip prefix-list LANX-OUT seq 5 permit 208.70.104.0/21
ip prefix-list LANX-OUT seq 10 deny 0.0.0.0/0 le 32
!
!
route-map LANX-IN permit 10
 match ip address prefix-list LANX-IN
 set local-preference 200
!
route-map DIALER-IN permit 10
 match ip address prefix-list DIALER-IN
!
route-map DIALER-OUT permit 10
 match ip address prefix-list DIALER-OUT
 set as-path prepend 14270 14270
!
route-map LANX-OUT permit 10
 match ip address prefix-list LANX-OUT